Answer:
c.
Step-by-step explanation:
We are given that

We have to find the value of C for which given function is even function.
We know that
Even function : If f(x)=f(-x) then the function is called even function.

Substitute the value then we get

We know that sin (-x)=-sin x, 
We know that Sin x is an odd function , therefore, option a is incorrect.
b.
Substitute the value then we get

It is an odd function.
Hence, option b is incorrect.
c.
Substitute the value then we get


We know that cos x is even function
Replace x by -x then, we get
....(cos (-x)=cos x)
Hence, the value of C=
for which given function will be an even function.
Answer:c.